In pipelines, especially gas pipelines, it is necessary to check the flow rate during continuous operation. To this end, use is made of measuring instruments which operate according to the differential pressure method. In this case, a metering orifice device is installed in the pipeline and the pressure inside the pipeline is measured upstream of the orifice of the metering orifice device and downstream of the orifice of the metering orifice device and the flow rate calculated from the difference. The measuring instrument is usually connected in this case to a 3-way or 5-way valve block. A connecting apparatus is installed in each case between the metering orifice device and the valve block so that the measuring instrument is in communication via the connecting apparatus with the interior of the pipeline upstream and downstream of the metering orifice device in each case and the pressure ratios can be measured.
Using such connecting apparatuses enables a direct installation of the valve block or of the measuring instrument on the metering orifice device. In comparison to remote, piped installation, with direct installation there is the advantage that measurement errors are significantly reduced and the measuring system becomes more reliable. Such connecting apparatuses have to ensure a permanently reliable sealing function during heavy duty at different temperatures and also in the event of severe vibrations occurring inside the fluid system.
A connecting apparatus, which is designed in one piece, is known from U.S. Pat. No. 4,974,308 and U.S. Pat. No. 4,920,626. In the end region facing the metering orifice device provision is made for a conical thread which is screwed into a corresponding thread of the metering orifice device until a sealing effect is provided. In the opposite end region, the connecting apparatus has a connecting flange which via a threaded connection is connected by a valve block to the measuring instrument.
Also known are connecting apparatuses which additionally have an integrated shutoff valve. In this case, however, the following problems ensue: Since the measuring instrument operates according to the principle of differential pressure measurement there is always a requirement for two connecting apparatuses which are to be arranged at a relative small distance from each other since the metering orifice device, to which are connected the connecting apparatuses, have to be of a relatively compact design in order to deliver reliable values. The shutoff valve is normally arranged perpendicularly to the longitudinal direction of the connecting apparatus and is constructionally higher than the distance between the two connecting apparatuses. As a result, with the first connecting apparatus installed the second connecting apparatus can no longer be screwed into the metering orifice device by rotation since the projecting shutoff valve collides with the first connecting apparatus when being screwed in.
There are also solutions in one piece in which the valve top part is supplied loose and after installation of the connecting apparatuses on the metering orifice device the client then has to install said top part. As a result, the following disadvantages ensue: The valve has to be installed at the work site so that a leak test or strength test by the valve manufacturer cannot be carried out and therefore no guarantee for leak tightness can be accepted either. If now during practical operation leaks occur, conflicts frequently occur between manufacturer and user since the leak can be caused by a faulty valve or a by faulty installation.
A valve apparatus according to the features of the preamble of claim 1 is known from U.S. Pat. No. 7,938,453 B2. The first connecting device is screwed into the metering orifice device via a conical thread. The second connecting device, which on the upper side has a connecting flange for the valve block, is screwed into the first connecting device, wherein the first connecting device has a corresponding blind hole opening with female thread and the second connecting device has a male thread.
This solution, however, requires an adjustment of the first and second connecting devices in relation to each other so that the connecting flange on the measuring instrument side can be brought into position.
An optimally integrated shutoff valve could also be installed at site only after installing the connecting apparatus.
In the case of two-part embodiments, in which the two connecting devices are connected by means of a flange, the shutoff valve can admittedly already be installed beforehand but there is the disadvantage that the connecting device, which has to be screwed into the metering orifice device, has to be already installed in position so that the connection to the valve block can be made.